The coccidian parasite Cryptosporidium parvum is a significant cause of human gastrointestinal disease worldwide. Infection with this parasite in immunocompetent individuals is frequently asymptomatic or associated with an acute self-limiting diarrheal illness. However in immunocompromised hosts such as patients with the acquired immunodeficiency syndrome (AIDS), infection with C. parvum may cause severe, unrelenting and often fatal diarrhea and wasting. There is no effective specific therapy for disease caused by this parasite. Our overall goal in the study of cryptosporidiosis is to identify and investigate parasite molecules involved in the initial host parasite interaction which may serve as targets of specific interventional therapies. This proposal is focused on two such molecules. The first of there is a Gal/GalNAc-specific lectin which was initially identified in C. parvum sporozoites. The second is a high molecular weight glycoprotein which wa identified using a monoclonal antibody, 4G12 that inhibited attachment of C. parvum sporozoites to host cells in vitro. The specific aims of the current proposal are a logical extension of the initial studies and are directed at further biochemical, molecular and functional characterization of these proteins and at further biochemical, molecular and functional characterization of these proteins and at determining their biological role in the host parasite interactions. The long term objective is to determine if infection by this parasite can be prevented or treated using either or both of these as targets of chemo- or immuno-therapy